Guideline 9: “Keep it simple.” Simplicity is a well known criterion which enhances the understandability of a language [8, 14, 22]. The demand for simplicity has several rea- sons. First, introducing a new language in a domain pro- duces work in developing new tools and adapting existing processes. If the language itself is complex, it is usually harder to understand and thus raises the barrier of intro- ducing the language. Second, even when such a language is successfully introduced in a domain, unnecessary complexity still minimizes the benefit the language should have yielded. Therefore, simplicity is one of the main targets in designing languages. The following more detailed Guidelines 10, 11, and 12 will show how to achieve simplicity.

Guideline 10: “Avoid unnecessary generality.” Usually, a domain has a finite collection of concepts that should be reflected in the language design. Statements like “maybe we can generalize or parameterize this concept for future changes in the domain” should be avoided as they unneces-

sarily complicate the language and hinder a quick and suc- cessful introduction of the DSL in the domain. Therefore, this guideline can also be defined as “design only what is necessary”.

Guideline 11: “Limit the number of language elements.” A language which has several hundreds of elements is obviously hard to understand. One approach to limit the number of elements in a language for complex domains is to design sublanguages which cover different aspects of the systems. This concept is, e.g., employed by the UML: different kinds of diagrams are used for special purposes such as structure, behavior, or deployment. Each of them has its own notation with a limited number of concepts.